Musnad Ahmad 658:86

Waki' narrated to us, Mis'ar narrated to us, from Thabit ibn 'Ubayd, from Yazid ibn al-Bara', from al-Bara' ibn 'Azib, who said: When we prayed behind the Messenger of Allah (peace and blessings of Allah be upon him), we liked—or you would like—to stand on his right side. He said: And I heard him say: "My Lord, protect me from Your punishment on the day You resurrect Your servants," or "gather Your servants."